1. Field of the Invention
This invention relates to internally apertured pressure-sensitive labels. More particularly, the invention relates to a method and apparatus for producing such labels adhered to a nonapertured liner.
2. Description of the prior art
Production of pressure-sensitive labels normally begins with a continuous flexible web of label material, which may for example be of film or coated paper, adhered to a coextensive continuous flexible liner, again of paper or film, by a pressure-sensitive adhesive which remains with the label web if the web is removed from the liner. The amount of force required to remove the labels from the liner is known as the release force, and is determined by the particular combination of web material, liner material and adhesive used, as is known to those skilled in the art. By suitable selection of web liner and adhesive, the release force can be varied to suit the label user's needs.
In the field of pressure-sensitive labels, there is an increasing demand for internally apertured labels--i.e. labels with one or more cut out areas within each label's perimeter. Heretofore the most common method of making such labels has been to die cut the aperture shapes through both the web and the liner, thereby forming separate aperture slugs consisting of both label material and liner material, and remove the cut out aperture slugs by suitable means. Buck U.S. Pat. No. 4,599,125 teaches a similar method and apparatus for producing pressure-sensitive reinforcing rings. In the Buck method, a first die cuts the circular shape of both the exteriors of the rings and the single central holes in each through the web but not the liner; the web surrounding the rings is then removed, leaving on the liner the rings and a separate central circular web slug in each. A second die then makes a central circular cut, of smaller diameter than the central circular web slug, through the liner under each ring only but not through the web, producing a circular liner slug to which the circular web slug is adhered. The web/liner slugs are then removed by a mechanical "picker" and disposed of suitably, for example through a vacuum hose. The resulting product includes a liner with separate pressure-sensitive reinforcing rings adhered thereto and with a hole through the liner concentric with the hole in each ring.
The main problem with methods such as taught by Buck--i.e. where the liner has open apertures under each of the label apertures, becomes evident automatic label dispensing operations. In such operations the label-containing web is fed from a supply roll to a point where the labels are to be applied to, e.g., containers which are passing the attachment point at a certain speed. Typically, at the attachment point the liner is caused to sharply change directions by passing it over a small radius rod or "breaker"; also at that point an appropriate blade-like member is often positioned to catch and lift the leading edge of each label as it arrives, with the result that the label is lifted from the liner and travels in an essentially straight path to the container surface where it is adhered by a suitable roller or the like. In very high speed dispensing operations, the presence of holes in the liner increases the likelihood of liner tearing at the separation point, for example because a corner in a hole acts as a stress raiser, or because a trailing edge of a hole lifts during the sharp bend of the liner and is caught by the label-separating blade. Moreover, where the labels and liner include a number of adjacent holes with only thin sections of material between them, the liner may not separate from the label at the thin sections, but instead a small piece of liner may tear loose and travel with the label, which causes improper adhesion of the label to the article to which it is applied.
The above-mentioned problems can largely be eliminated by providing internally apertured labels on a non-apertured liner. The basic cutting mechanisms of such a process are known; they simply include die cutting both the label periphery and the internal aperture shapes through the web but not through the liner. However, removal of the cut-out internal aperture slugs thus formed has proved problematic. It is, of course, possible to remove the slugs by hand if extremely slow production speed and high costs can be tolerated; where a label includes a number of small internal apertures, such drawbacks would naturally be exacerbated in a manual operation.
Gutow U.S. Pat. No. 4,328,057 discloses a mechanized method and apparatus for producing internally apertured pressure-sensitive labels on a non-apertured liner which improves the speed and economy of production, but it also presents problems. In Gutow a first die cuts the aperture shape through the web only and not through the liner, forming a separate aperture slug. The web/liner then travels to and over a breaker, at which point the aperture slug lifts from the liner and is removed, via a nozzle and conduit, by a vacuum cyclone separator; the remaining web and liner are guided around suitable guide rollers to a second die, which cuts the outer periphery of the label through only the web, and thence to a take-up point where the "ladder" of scrap web surrounding the label is removed, leaving the liner with only the labels attached. In order to minimize adhesion of the removed aperture slugs to one another or the vacuum conduit, Gutow applies a silicone oil spray to the slugs as they enter the vacuum nozzle.
The Gutow method does produce internally apertured pressure-sensitive labels on a non-apertured web, but it is has several shortcomings. First, the length of travel path required between the aperture cut point and the periphery cut point because of the need to pass the web/liner over the breaker, coupled with the bends undergone by the web/liner in travelling that path, can cause a loss of precision in registry between the aperture location(s) and the label periphery; such loss of precision may be acceptable in producing a label design having a single relatively large and regularly-shaped aperture, but can be fatal where a number of small and/or precisely located apertures are required in the label. Second, Gutow's use of a silicone oil mist coating and vacuum removal of the aperture slugs not only requires two added sets of delivery and/or conduit systems, one for the oil and one for the vacuum, but also would likely be messy and ineffective for a label design having a plurality of small aperture slugs to remove. Finally, the Gutow slug removal system does not lend itself to high speed production of multi-apertured pressure-sensitive labels where the aperture sizes are small and/or varied.
In view of the foregoing, a need exists for a method and apparatus that can produce internally apertured pressure-sensitive labels adhered to a non-apertured liner at high rates of production.